1. Field of the Invention
The present invention relates to a disc reproducing apparatus and a disc reproducing method for reading information recorded on an optical disc such as a CD, a CD-ROM, or a DVD-ROM.
2. Description of the Related Art
Generally, in a disc reproducing apparatus that reproduces a signal from an optical disc such as a CD, a CD-ROM, or a DVD-ROM in a constant linear velocity recording method, when the frequency of an input signal is in a capture range of a PLL (Phase-Locked Loop) circuit, an output signal of an optical pickup can be demodulated at a proper timing.
However, in such a disc reproducing apparatus, when a signal is reproduced at the maximum reproducing speed, it takes a time period after the stop state of the optical disc until the disc is rotated at the maximum reproducing speed by a disc motor. Thus, while the disc motor is accelerating the rotating speed of the optical disc, the frequency of a signal that is read from the optical disc by the optical pickup to the PLL circuit varies time by time.
However, the capture range of the PLL circuit is optimized for an input signal at the maximum reproducing speed. Thus, the disc reproducing apparatus cannot properly read data until the rotating speed of the optical disc becomes fast and the frequency of an input signal of the PLL circuit is in the capture range.
This invention is disclosed in Japanese Patent Application No. 10-109138 filed on Apr. 20, 1998, and the entire disclosure thereof is incorporated herein by reference.
An object of the present invention is to provide a disc reproducing apparatus and a disc reproducing method that can correctly read information from an optical disc even in a transient state such as an accelerating/decelerating state of the optical disc.
A first aspect of the present invention is a disc reproducing apparatus, comprising an optical pickup for reading a signal from a disc, a clock signal reproducing circuit for reproducing a clock signal so as to reproduce data from the signal read by the optical pickup, a signal processing circuit for reproducing data with the clock signal reproduced by the clock signal reproducing circuit, and a range shifting means for shifting a capture range of the clock signal reproducing circuit.
According to the present invention, the capture range of the clock signal reproducing circuit can be shifted in a time period at least after an occurrence of a reproduction command until data is reproduced from the disc at a target linear speed corresponding to the reproduction command.
Thus, according to the present invention, in the state that the rotating speed of the disc varies time by time, the frequency of an input signal can be placed in the capture range that can be shifted by the clock signal reproducing circuit. Consequently, even in a transient state such as an accelerating/decelerating state of the disc, data can be properly reproduced from the disc.
A second aspect of the present invention is a disc reproducing apparatus, comprising an optical pickup for reading a signal from a disc, two clock signal reproducing circuits for reproducing clock signals so as to reproduce data from the signal read by the optical pickup, the two clock signal reproducing circuits having different capture ranges, two signal processing circuits for reproducing data with the clock signals reproduced from the two clock signal reproducing circuits, the two signal processing circuits being disposed corresponding to the two clock signal reproducing circuits, a selecting means for selecting reproduction data that has been correctly reproduced by one of the two signal processing circuits, and a range shifting means for shifting the capture range of the clock signal reproducing circuit corresponding to a first signal processing circuit of the two signal processing circuits when the selecting means selects reproduction data reproduced from a predetermined one as a second signal processing circuit of the two signal processing circuits.
In other words, according to the present invention, while the first signal processing circuit with a high (low) capture range is correctly reproducing data, the capture range of the second signal processing circuit (with a low (high) capture range) is changed to a capture range that is higher (lower) than the capture range of the first signal processing circuit. Thus, data can be properly reproduced from the disc corresponding to the chronological variation of the linear velocity of the disc. Consequently, even in a transient state such as an accelerating/decelerating state of the disc, reproduction data can be successively output.
A third aspect of the present invention is a disc reproducing apparatus, comprising an optical pickup for reading a signal from a disc, a plurality of clock signal reproducing circuits for reproducing clock signals so as to reproduce data from the signal read from the disc by the optical pickup, the plurality of clock signal reproducing circuits having different capture ranges, a plurality of signal processing circuits for reproducing data with the clock signals reproduced from the plurality of clock signal reproducing circuits, the plurality of signal processing circuits being disposed corresponding to the plurality of clock signal reproducing circuits, and a selecting means for selecting reproduction data that has been correctly reproduced by one of the plurality of signal processing circuits.
In other words, according to the present invention, since correct reproduction data is selected from outputs of a plurality of clock signal reproducing circuits with different capture ranges, data can be properly reproduced from the disc corresponding to the chronological variation of the linear velocity of the disc. Consequently, even in a transient state such as an accelerating/decelerating state of the disc, reproduction data can be successively output.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings.